In certain circumstances, it is desirable to inject medication directly into human tissue. Typically, syringes are used to inject selected doses of medicaments into a patient. Hypodermic syringe includes a syringe barrel having opposed proximal and distal ends. A cylindrical chamber wall extends between the ends and defines a fluid receiving chamber. The proximal end of the syringe barrel is substantially open and receives a plunger in sliding fluid tight engagement. The distal end of the syringe barrel includes a passage communicating with the chamber. A needle cannula may be mounted to the distal end of the syringe barrel, such that the lumen of the needle cannula communicates with the passage and the chamber of the syringe barrel. Movement of the plunger in a proximal direction draws fluid through the lumen of the needle cannula and into the chamber. Movement of the plunger in a proximal-to-distal direction urges fluid from the chamber and through the lumen of the needle cannula.
Medication to be injected with the prior hypodermic syringe often is stored in a vial having a pierceable elastomeric seal. Medication in the vial is accessed by piercing the elastomeric seal with the needle cannula. A selected dose of the medication may be drawn into the chamber of the syringe barrel by moving the plunger a selected distance in a proximal direction. The needle cannula may be withdrawn from the vial, and the medication may be injected into a patient by moving the plunger in a distal direction.
Some medication, such as insulin is self-administered. The typical diabetes patient will require injections of insulin several times during the course of a week or day. The required dose of insulin will vary from patient to patient, and for each patient may vary during the course of the day and from day to day. Usually, each diabetes patient will establish a regimen that is appropriate for his or her own medical condition and for his or her lifestyle. The regimen typically includes some combination of a slow or medium acting insulin and a faster acting insulin. Each of these regimens may require the diabetes patient to periodically self-administer insulin in public locations, such as places of employment or restaurants. The required manipulation of the standard hypodermic syringe and vial can be inconvenient and embarrassing in these public environments.
Medication delivery pens have been developed to facilitate the self-administration of medication. An example of one such medication delivery pen is described in U.S. Pat. No. 5,279,585 (Balkwill), which includes a vial holder into which a vial of insulin or other medication may be received. There remains a need for a medication delivery pen that allows a user to easily set and correct a dosage prior to delivery.